1835.] Porphyritic Greenstone Rocks. 279 



united with greenish-black hornblende, which has two 

 faces of cleavage cutting each other at an angle of 124 . 

 The union of this hornblende with the hypersthene is, how- 

 ever, regular; because, the main axes of the four-sided 

 prisms, which the cleavage faces of the hornblende and 

 hypersthene form, as well as that through the sharp edges 

 of the hornblende prisms, and that through the blunt edges 

 of the hypersthene prisms, are parallel. Such is the case 

 in the hypersthene of Penig, and in many rolled masses at 

 Berlin, yet not so distinct as in the diallage of gabbro, or 

 the augite of the augite porphyry, yet to be described, but 

 is probably of the same origin, and apparently not original, 

 but proceeds from an incipient alteration of the hypersthene 

 described. Besides the usual constituents, we meet with 



Olivine, which occurs in large grains, of an olive-green 

 colour (Elfdalen in Sweden). It is distinguished from 

 hypersthene, by the almost total absence of faces of cleav- 

 age, its infusibility before the blow-pipe, and its colour. 



Mica, in pinchbeck-brown scales. 



Apatite, in thin, long, white, six-sided prisms, which are 

 distributed among the other ingredients. 



Titaniate of Iron, in iron— black, metallic, splendent, 

 magnetic grains, which are distinguished from magnetic 

 iron ore by the red colour which they impart to salt of 

 phosphorus when fused before the blow-pipe. 



Iron pyrites, intermixed, generally in small quantities. 



The hypersthene rock occurs in greater or smaller grains ; 

 sometimes the diameter of a compound grain exceeds several 

 inches ; at other times, it is so finely granular as to appear 

 almost homogeneous. In general, the mixture of labrado- 

 rite, predominates over the hypersthene. Olivine and iron 

 pyrites, where these ingredients occur, are present only in 

 very small quantity. Titaniate of iron, on the contrary, is 

 found in many varieties of hypersthene, so abundantly as 

 to present the appearance of being an essential constituent 

 (Elfdalen, and rolled masses, in the vicinity of Berlin). 

 In other varieties, it is entirely absent (Paul's Island). 



The hypersthene rock of Elfdalen, which contains much 

 titaniate of iron interspersed through it, melts in a charcoal 

 crucible into a grayish black mass, on the bottom of wliich 



